It's a bipedal animal with an axe. Things like that are why the Beast-Warrior type exists in the first place... "Beast" doesn't inherently imply mammal. (Indeed, there's a Beast-type shark, a turtle, several birds, etc.) And many monsters could fit under many different types. Catapult Turtle could legitimately be an Aqua, Reptile or Machine for instance.
Actually it's a bipedal dragon with an axe.
Beasts are usually huge mammals. The equivalent word for beast is "therium" which derives from the Greek word "therio" probably even Latin origins (doesn't matter). The ancestors of the mammals you are seeing today are considered "beasts" since their scientific name contained the term "therium". I don't think anyone described dinosaurs as beasts though.
In the other hand, the typing of Catapult Turtle is legitimately correct, besides that even Reptile is proper. Having a catapult attached to it doesn't make it a machine since it hasn't that complex function.
...Have you actually looked at Catapult Turtle? It's VERY clearly a robotic turtle, not a living creature. Its neck and jaw are very obvious, even moreso in the anime, and it has glowing red eyes.
There's another explanation if the above didn't satisfy you.
If they placed it as a Machine it would be controversial because it would be a WATER monster that loses stats when "Umi" is on the field. The fact that already that case exists with Metal Fish is quite upseting.
Umi wasn't any more notable than any other Field Spell at the time Catapult Turtle (or Metal Fish or Mech Bass for that matter) was released. Also, the first cards to benefit from Umi (The Legendary Fisherman and Deepsea Warrior) weren't affected by it in the first place, so synergy with Umi obviously wasn't even a concern.
Why do you compare this case with Catapult Turtle? Both of those types you mentioned are appropriate. Classifying a darn dragon as a beast warrior it's utterly crap.
A dragon is an animal. "Beast" is a term for an animal (and regardless of the above arguments, no definition of "beast" even IMPLIES it's mostly intended for mammals.) And heck, it's proven as such even in YGO canon with Ra's Summon chant.
It's a mythological animal. I guess you don't consider dead animals to be animals either, or extinct ones.
Hint: Anything that is/was alive (or depicted as such, if fictional, unless you want to argue Bugs Bunny isn't an animal either) that isn't a plant is considered an animal, regardless of whether you can comprehend that or not.
The words are mostly synonymous. It did indeed used to refer to "created beings", but that usage is virtually extinct. Indeed, most current definitions of the word "creature" are along the lines of "a living creature, either an animal or a human". I'll point to Wikipedia's page on legendary creatures's definition as a practical example: "a fictitious, imaginary and often supernatural animal"
Wiki articles/pages are widely known to get altered quite often, so don't get surprised when the word "animal" gets replaced by the word "creature".
Besides your argument is just another reason to limit the whole typing concept since you are distinctly claim that all the dragons should be considered beasts so you are contradicting with your self.
Except that article's referred to animals (through several rewrites and revisions, might I add) for the last five years.
And you're right. You could technically consider basically any monster that's a living being and not a plant to come under the Beast type. But they chose not to do that. The way you're arguing is like saying "a frog's an amphibian, not an animal", which is just wrong.
Frogs are contained in the Aqua type which is the most properly correct for them.
My arguments are based in pure logic.
The 80% of the monsters that they put in the Beast type depict mammals. Then, they randomly put without giving much of a thought less than 5 monsters that have apparent reptilian and dragonic visual characteristics.
It's a sign of lazyness to me.